The present invention relates to a cylinder head of a piston engine, which has a thermal insulation component made by sintering from ceramic materials, and which has openings for valves, spark plugs or injection nozzles.
For the prevention of wall losses, it has previously been proposed in German Offenlegungsschrift No. 2,821,506 to cover the inside surface of a cylinder head with a laminated insulating plate. The laminated insulating plate described consists of the actual insulating layer and a metal backing plate tightly joined thereto. The insulating layer faces the combustion chamber and consists either of vitreous fused silica, or of silicon nitride or silicon carbide, and it is either fused or sintered onto the metal backing plate, or the insulating layer is of laminated construction with an especially porous middle layer which is formed preferably of spheres of the insulating material. In such a cylinder head it is disadvantageous that the usual arrangement of several separate openings for valves, spark plugs and injection nozzles is difficult to achieve, and consequently it is necessary to have only a single opening in the laminated insulating plate. Another disadvantage lies in the complexity of construction, especially in the fact that the actual insulating layer, on account of its low stength, requires a metal backing plate.
German Offenlegungsschrift No. 3,039,718 disclosed a cylinder head in which a refractory body consisting of silicon nitride is inserted into a thermal insulation component consisting of aluminum titanate, and this laminate is shrink-fitted into a metal supporting body, which in some cases is formed by the cylinder head. The refractory body, which forms the bottom of the cylinder head, faces the combustion chamber and protects the thermal insulation component against mechanical stress. The thermal insulation component is in the form of a circular disk having a marginal rim to accommodate the refractory body. Here, again, the disadvantage is the laminated construction of the individual components consisting of different materials, which is necessitated by the low strength of aluminum titanate. Another disadvantage is that the laminate consisting of the thermal insulation component and the refractory body cannot be subjected to clamping pressure, and instead must be provided with a supporting body to protect the aluminum titanate.
In the publication by Woods/Oda, "PSZ"-Ceramics for Adiabatic Engine Components, published in the SAE Technical Papers Series, cylinder heads having shrink-fitted plates of partially stabilized zirconium oxide (PSZ) have been disclosed, but they have not found acceptance because the thermally induced tensions due to the high thermal expansion of zirconium oxide, especially in the area of the valve bores, result in cracking, particularly in the radial direction.
In short, in the state of the art, cylinder heads having thermal insulation components are known, in which these components are made from materials which have either a low thermal expansion and low thermal conductivity combined with low strength (aluminum titanate), or from materials which have a low thermal conductivity and a high strength, but also have a high thermal expansion (zirconium oxide). None of these known proposals have proven adequate.
The object of the present invention lies in the development of a cylinder head which will have a good insulating action on the combustion chamber side, while at the same time demanding that the component that provides the insulation have a long useful life, even under intensified stress. The invention intends especially to make available a cylinder head having a thermal insulation component which will have excellent strength for resisting mechanical forces and especially thermally induced tensions.
It is also the aim of the invention to make available a thermal insulation component having a simple construction, which is to be installed in the cylinder head in a simple and easy manner, and which at the same time will be given a firm seating in the cylinder head. The invention intends also to create a component which will render unnecessary the separate manufacture and assembly of valve seats made from another material, and will make it possible to form the valve seats directly in the thermal insulation component.